The present invention relates to the field of ecology and more particularly to the remediation of environmental contaminants by enzymatic reduction and oxidation.
Contamination of the air, water and soil is a severe problem endangering the lives of many plants and animals, including humans. Many attempts have been made to reduce contamination by either preventing escape of the contaminants into the environment, containing the contaminants at one site, or treating the contaminants in some way to make them less harmful.
Extensive soil, water, sediment and aquifer contamination has occurred from the manufacture and widespread use of explosives by both civilians and the military. For example, the compound 2,4,6-trinitrotoluene (TNT) is a highly oxidized nitroaromatic that is stable on soil surfaces in the environment for as many as 40 years.
Currently, the preferred technology for remediating TNT-contaminated soil is by burning the soil and then cashing the incinerated soil in an enclosure for an indefinite amount of time. The burning treatment is expensive, costing $300-400 per ton, and, for a large contaminated site encompassing several acres, could cost tens of millions of dollars.
Scientists have shown that it is possible to degrade certain organic pollutants in soil through oxidation/reduction (redox) reactions. The goal has been to chemically or biologically oxidize or reduce the contaminants or functional moieties of the contaminants to innocuous compounds or compounds that can be easily degraded and eliminated from the soil by known processes.
Nitroorganic Pesticides
Environmental contaminants that have been partially degraded through redox reactions include nitroaromatic pesticides such as parathion, methyl parathion, trifluralin, profluralin, benefin, nitrofen and pentachloro-nitrobenzene as described by Williams, P. P., Residue Rev. 66:63-135 (1977); Wahid, P. A. et al., J. Environ. Qual. 9:127-130 (1980); Graetz, D. A. et al., J. Water Poll. Control Fed. 42:R76-R94 (1970); Adhya, T. K. et al., J. Agric. Food Chem. 29:90-93 (1981); Camper, N. D. et al., J. Environ. Sci. Health B15:457-473 (1980); Golab, T. et al., J. Agric. Food Chem. 27:163-179 (1979); Probst, G. W. et al., J. Agric. Food Chem. 15:592-599 (1967); Willis, G. H. et al., J. Environ. Qual. 3:262-265 (1974); Golab. T. et al., J. Agric. Food Chem. 18:838-844 (1970); Lee, J. K. et al., Misaengmul Hakhoe Chi. 20:53-66 (1982); Qian, W. W. et al., Huanjing Kexue 3:36-39 (1982); and Murthy, N. B. K. and D. D. Kaufman, J. Agric. Food Chem. 26:1151-1156 (1978).
These nitroaromatic pesticide treatments generally involve the anaerobic transformation of the pesticides to reduced compounds by unidentified substances naturally present in the soil. However, the reduced products of nitroaromatic pesticide degradation include anilines and other compounds that are considered to be environmental hazards.
Nitroorganic Explosives
Many unsuccessful attempts have been made to oxidize the explosives 2,4,6, -trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX) and N-methyl-N-2,4,6-tetranitroaniline (Tetryl), nitrocellulose and red water (a by-product of TNT production) to innocuous products. None have found any practical or commercial application because these compounds are highly oxidized, and further oxidation generally requires excessive amounts of energy. Attempts have also been made to remediate these compounds microbially by reduction under anaerobic conditions. (Alvarez, M. et al., Enzyme Catalyed Transformation of 2,4,6-Trinitrotoluene, Abstracts of the General Meeting of the Am. Soc. for Microbiology 91:217 (1991)) However, the reduction products of these compounds include the corresponding amines and several other less well defined hydroxyazo compounds. The analogs of these reduction products are potential carcinogens and are considered to be environmentally hazardous.
Halogenated Hydrocarbons
Halogenated hydrocarbons as a class of compounds are one of the most ubiquitous pollutants in the United States. They have been and still are widely used in many industries as cleaning solvents, refrigerants, fumigants and starting materials for the syntheses of other chemicals. Because of their extensive use, there are hundreds of contaminated groundwater and landfill sites in the United States, many of which are superfund sites for which there is no inexpensive, effective remediation technology available. Also, industrial waste treatment technology is expensive and not always effective.
In contaminated ground water systems, the water is pumped out of the reservoir and treated with the "air stripping" treatment procedure. Halogenated hydrocarbons have also been remediated by a photolysis procedure wherein contaminated soil or sediment is placed on an oxide film and irradiated with concentrated sunlight to remove chloride atoms. These procedures are expensive and only successful if all of the contaminated material has been successfully removed from the site of contamination. Effective in situ treatment is not practiced because of a lack of treatment technology. Bioremediation has not been successful because maintenance of a viable microorganism population is not generally feasible in subsurface ecosystems. Chemical remediation processes have not been utilized because of the delivery of large amounts of the necessary chemicals and problems associated with groundwater hydrology.
Bioremediation has received considerable attention as an in situ remediation process of contaminated waste sites. The parent pollutants, however, are often resistant to degradation and must first be transformed to more degradable compounds for the processes to be effective. Although many microorganisms have been isolated that are capable of degrading halogenated hydrocarbons in the laboratory, they are not always effective when ported to the field situation.
Cyano Compounds
Aliphatic and aromatic cyano compounds are used as solvents and intermediates in the chemical industry in a variety of synthetic processes including textiles and pesticides. For example, acrylonitrile is a high production compound with output exceeding more than 2.3 billion pounds a year. These compounds can enter the environment through manufacturing waste waters and from the polymers of which they are associated and as a result of applications of pesticides such as dichlobneil (2,6-dichlorobenzonitrile) and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile).
Biodegradation of selected cyano compounds has been demonstrated in waste water treatment systems. In soils, however, degradation is more difficult and high concentrations of the pollutants are often not readily degraded. Also, not all soils, in particular sandy soils, have the necessary microbial populations to degrade nitrites.
Anisoles
Anisoles are used as intermediates in the chemical industry for the manufacture of a large number of polymer, dye and pesticide compounds. These compounds find their way into the environment through point source and non-point source pathways. For example, the pesticide methoxyclor has been one of the most widely used pesticides in the United States. In general, anisoles are hard to degrade because the methyl-oxygen bond is very strong.
Other Contaminants
Remediation of other environmental contaminants such as metals has also been largely unsuccessful. Metal contaminants have been treated by the "pump and treat" procedure wherein water is pumped out of the contaminated area and passed over a tube containing titanium to transform the contaminants to compounds that are less hazardous to the environment. The "pump and treat" method is very costly, is only applicable for removal of volatile contaminates from surface water or aquifers, and is not successful until the source of the contamination is depleted.
It would be of great environmental benefit to have an inexpensive method of degrading contaminants in soils, waters, sediments, and aquifer materials that results in products that are environmentally acceptable.
It is therefore an object of the present invention to provide an improved method of remediating environmental contaminants.
It is a further object of the present invention to provide a method of remediating environmental contaminants that can be carried out in situ and in batch reactors.
It is a further object of the present invention to provide a composition for rapid reduction of contaminants.
It is a further object of the present invention to provide a process for the production of contaminant-reducing agents from soil.
It is a further object of the present invention to provide a method of remediating nitro-, halogenated-, cyano-, methoxy-organic, and metal contaminants from the environment.
It is a further object of the present invention to provide a method of oxidizing reduced pollutants.
It is a further object of the present invention to provide a method of remediating environmental contaminants that is cost-effective.
It is a further object of the present invention to provide a method of remediating soils, sediments, and aquifers that maintains the integrity of the environmental compartment.